1. Field of the Invention
The present invention relates to a terminal capable of data communication with a wide area network (i.e., WAN) by radio communication through a Base Transceiver Station (i.e., BTS), and relates to an intermediary device capable of relaying data between the terminal and WAN. These devices are useful in data communication between a mobile device and a server on the Internet.
2. Related Art
In these years, communication with a WAN such as the Internet using a terminal such as a cell phone, i.e., mobile data communication is being used. This communication can be realized in a manner that a terminal communicates with a BTS, for example, a first BTS, using radio transmission and the BTS conducts data communication with the WAN through a segment, for example, a first segment, to which the first BTS belongs.
Generally, a BTS uses one address, among address space allocated to a segment to which the BTS belongs, for conducting data communication with the WAN. Since address space allocated to each segment is different than the others, when the first BTS, which communicates with the terminal, is switched to a second BTS due to the movement of the terminal, the second BTS belongs to a second segment different from the first to which the first BTS belongs, and the terminal no longer uses the address which was used while the terminal communicated with the first BTS. Therefore, the terminal uses a new address among address space in the second segment.
In the above-mentioned situation, that is, when the address used by the terminal is changed, a server communicating with the terminal on the WAN no longer identifies the terminal, thereby losing communication between the terminal and the server.
To avoid losing communication, mobile IP (Internet Protocol) has been employed. The mobile IP is used for ensuring data communication in the following manner. The terminal is allocated a home address in a predetermined segment with which the terminal communicates. When the terminal moves and has to change a segment from the predetermined one to the other, the data required by the terminal is sent to the home address. Then, a host, called a home agent, transfers the data in the home address to the terminal.
However, a data transmitting route is complicated when the terminal leaves the predetermined segment, thereby lowering the communicating efficiency. Moreover, the special device, such as the home agent, has to be equipped, and therefore, a structure of the network is inevitably complicated.